control/controlclient: run SetControlClientStatus in goroutine

We have cases where the SetControlClientStatus would result in
a Shutdown call back into the auto client that would block
forever. The right thing to do here is to fix the LocalBackend
state machine but thats a different dumpster fire that we
are slowly making progress towards.

This makes it so that the SetControlClientStatus happens in a
different goroutine so that calls back into the auto client
do not block.

Also add a few missing mu.Unlocks in LocalBackend.Start.

Updates #9181

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/local.go

@@ -1396,6 +1396,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 	wantRunning := prefs.WantRunning()
 	if wantRunning {
 		if err := b.initMachineKeyLocked(); err != nil {
+			b.mu.Unlock()
 			return fmt.Errorf("initMachineKeyLocked: %w", err)
 		}
 	}